Oscillating circuit

ABSTRACT

An oscillating circuit comprising a Schmitt circuit, a grounded capacitor connected to the input side of the Schmitt circuit and a control circuit connected to the output side of the Schmitt circuit for controlling the charging and discharging of the capacitor.

Em A. iJnrted States atent 1 [111 39 3mm Kubo et al. 1 ay i, 1973 [54]OSCILLATING CIRCUIT [58] Field of Search ..33l/l ll; 307/290 [75]Inventors: Noriyoshi Kubo; Kazuhiro Nakamura; Yoshinori Endo, all of[56] References C'ted Yokohama; Takeshi Katano; Eisuke Ichinohe, both ofOsaka, all of UNITED STATES PATENTS Japan 3,289,103 11/1966 Campman..33l/l1l [73] Assigneez fiztslglsrja lilllaectllr'lic Industrial Co.,Primary Examiner john Kominski p Att0rneyStevens, Davis, Miller & Mosher[22] Filed: Sept. 16, 1971 21 Appl. No: 131,034 [571 ABSTRACT Anoscillating circuit comprising a Schmitt circuit, a [30] ForeignApplication Priority Data grounded capacitor connected to the input sideof the Schmitt circuit and a control circuit connected to the Sept. 18,1970 Japan ..45/82356 Output Side of the Schmitt circuit for controllingthe charging and discharging of the capacitor. [52] US. Cl ..33l/11l,307/290 {51] Int. Cl. ..H03k 3/295 1 Claim, 3 Drawing Figures PATENTEUH973 3.731.228

OFF 0/v VOLTAGE &

- T/ME OSCILLATING CIRCUIT FIELD OF THE INVENTION This invention relatesto oscillating circuits and, more particularly, an oscillating circuitusing a Schmitt circuit which may be readily integrated into asemiconductor integrated circuit and may be made to serve as a variableoscillator.

SUMMARY OF THE INVENTION An object of the invention is to provide anoscillating circuit comprising a Schmitt circuit, a grounded capacitorconnected to the input side of the Schmitt circuit and a transistorcontrol circuit connected to the output side of the Schmitt circuit forcontrolling the charging and discharging of the grounded capacitor.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a circuit diagram showing anembodiment of the oscillating circuit according to the invention.

FIG. 2 shows a hysteresis character of the oscillation of the circuit ofFIG. 1.

FIG. 3 is a graph showing the terminal voltage across the charging anddischarging capacitor.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a preferredembodiment of the oscillating circuit according to the invention. Ituses a Schmitt circuit including transistors TR,, and TR and resistors RR and R A grounded capacitor C is connected to the input side of theSchmitt circuit. The charging and discharging of the capacitor C iscontrolled through a circuit consisting of a transistor TR resistors Rand R and a diode D It is discharged through a discharging resistor RThe resistor R R and R are connected to a power supply V In theoperation of the circuit described above, when the transistors TR TR andTR are respectively off, on and off, the capacitor C 1 is chargedthrough the loop of power source V resistors 5 and 6 and capacitor C Atthis time, the voltage drop V across the resistor R is (ignoring thesaturation voltage of the transistor TR Thus, the terminal voltageacross the capacitor C reaches a predetermined value given as c 4/( 4+s)' cc BE (where V is the potential difference between the base andemitter of the transistor TR As soon as this predetermined terminalvoltage across the capacitor C is reached, the transistor TR istriggered. At this instant,

V,, R,/(R +R V +0.6 V (2) (where 0.6 V represents the potentialdifference between the base and emitter of the transistor TR Also, forthe base voltage on the transistor TR, at this instant 4/( 2+ 4) ar VCE)VBE c (where V is the potential difference between the collector andemitter of the transistor TR and equal to the base-emitter voltagethereof). Upon triggering of the transistor TR the transistor TR is cutoff to trigger the transistor TR;,.

At this time, if Z Z Z: where Z is the impedance provided by resistor Rtransistor TR and diode D Z is the impedance provided by resistor R andZ is the impedance provided by transistor TR and resistor R thecapacitor C is discharged through a loop of resistor R transistor TR;,and diode D and through another loop of resistor R As soon as theterminal voltage of the capacitor C, being discharged is reduced to acertain prescribed level, the transistor TR is cut off, triggering thetransistor TR to cut off the transistor TR As a result, re-charging ofthe capacitor C starts.

If the resistance of the resistor R is equal to the resistance of theresistor R the charging and discharging of the capacitor C take the sameperiod. However, if the former resistance is selected to be greater thanthe latter resistance, the base potential of the transistor TR at theinstant of its triggering is different from the level at the instant ofits cut-off. Thus, the oscillation involves a hysteresis decay as shownin FIG. 2.

In this case, the capacitor C, is charged and discharged in a manner asshown in FIG. 3. In the Figure, V and V represent respective minimum andmaximum levels of the terminal voltage across the capacitor C and fromequations 2 and 3 and The resistor R serves to stabilize the dischargingof the capacitor C and hence the oscillation of the oscillating circuitaccording to the invention. Without the resistor R the discharging ofthe capacitor C through the path of resistor R transistor TR, and diodeD is likely to be suddenly subjected to very unstable conditions.

As has been described, according to the invention a hysteresis characteris imparted to the operation of the Schmitt circuit for on-offcontrolling the control transistor TR controlling the charging anddischarging of the capacitor C so that reliable oscillation can beensured. Also, all the components parts which are relatively small innumber may be readily integrated into a semiconductor integrated circuitexcept for the capacitor C Further the oscillation frequency may bereadily made variable by using a variable capacitor for the capacitor CWe claim:

1. An oscillating circuit comprising a Schmitt circuit including a pairof transistors connected in cascade,

a capacitor connected between the input of said Schmitt circuit andground,

a control transistor coupled to the output of said Schmitt circuit forcontrolling the charging and discharging of said capacitor, the on-offoperation of said control transistor being controlled by the output ofsaid Schmitt circuit,

connecting circuit means connected between said capacitor and saidcontrol transistor, said connecting circuit means being a portion of acharging circuit and also a portion of a first discharge circuit,

a second discharge circuit for said capacitor including a resistorconnected in parallel with said capacitor, and

a diode connected in series with said control transistor, saidconnecting circuit means, control transistor and diode comprising saidfirst discharge path, said first discharge path having a low impedancewith respect to the impedance of said 5 second discharge circuit.

UNITED STATES PATENT OFFICE CERTIFICATE OF COEUHON Patent NO. 3,731,228v Dated May 1, 1973 InVentor(s) Noriyoshi Kubo et a1 It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Col. 2, line 31, formula should read:

= R4) V VBE Signed and sealeglthis 27th day of November 1973 (SEAL)Attest:

EDWARD M.FLETCHE R;JR. RENE D. TEGTMEYER,

Attesting Officer Acting Commissioner of Patents )RM Po-wso (10-69)uSCoMM-Dc 6O376-P69 U.S, GOVERNMENT PRINTING OFFICE: I969 36-334.

1. An oscillating circuit comprising a Schmitt circuit including a pairof transistors connected in cascade, a capacitor connected between theinput of said Schmitt circuit and ground, a control transistor coupledto the output of said Schmitt circuit for controlling the charging anddischarging of said capacitor, the on-off operation of said controltransistor being controlled by the output of said Schmitt circuit,connecting circuit means connected between said capacitor and saidcontrol transistor, said connecting circuit means being a portion of acharging circuit and also a portion of a first discharge circuit, asecond discharge circuit for said capacitor including a resistorconnected in parallel with said capacitor, and a diode connected inseries with said control transistor, said connecting circuit means,control transistor aNd diode comprising said first discharge path, saidfirst discharge path having a low impedance with respect to theimpedance of said second discharge circuit.